The present invention relates to an electronic device adapted for operation with a P1394 serial bus, for example, and more particularly to a control technique intended to save power in such an electronic device.
Conventionally designed is a system including electronic devices such as a personal computer (which will be hereinafter referred to as "PC"), a digital video tape recorder (which will be hereinafter referred to as "D-VTR"), and a digital television receiver (which will be hereinafter referred to as "D-TV") together through a P1394 serial bus to perform communication of a digital video signal, digital audio signal, and control signal between these electronic devices.
FIG. 12 shows an example of such a system. Referring to FIG. 12, electronic devices A to D represent a PC, D-VTR, etc. as mentioned above. The electronic devices A and B are connected together through a P1394 serial bus cable 41; the electronic devices B and C are connected together through a P1394 serial bus cable 42; and the electronic devices C and D are connected together through a P1394 serial bus cable 43.
Each P1394 serial bus cable incorporates two pairs of twisted pair cables with shields (not shown). One of the two pairs of twisted pair cables is used for transmission of data, and the other pair is used for transmission of a strobe signal.
As shown in FIG. 12, each electronic device includes a physical layer controller 44 and a CPU and link layer controller 45 as a basic configuration for performing communication with the corresponding P1394 serial bus. The physical layer controller 44 has a function including initialization of the bus, encoding/decoding of data, and arbitration. The CPU and link layer controller 45 has a link layer control function including generation/detection of an error correction code and generation/detection of a packet, and an application layer function.
In each electronic device having the above configuration, when a power-supply plug (not shown) of the electronic device is inserted into an AC receptacle, a power-supply voltage is supplied to the physical layer controller 44. Accordingly, the power-supply voltage is always supplied to the physical layer controller 44 irrespective of whether or not the bus is used, resulting in undue consumption of power.
This problem may be solved by on/sleep controlling the power-supply voltage to be supplied to the physical layer controller with operation from a user. According to this method, the physical layer controller can be powered on only when the electronic device uses the bus, thereby saving a power consumption. However, when the physical layer controller in the electronic device B shown in FIG. 12, for example, is in a sleep mode, the communication between the electronic device A and the electronic device C cannot be effected unless the user manually sets the electronic device B to an on mode.